1. Field of the Invention
The present invention relates to a method for manufacturing a optical fiber assembly with a polished end face, an end face polishing apparatus and a method for examining the end point of an end-face polishing process of the optical fiber. It also relates particularly to a method for manufacturing a optical fiber assembly with a polished end face, an end face polishing apparatus and a method for examining the end point of an end-face polishing process of the optical fiber for improving the connection characteristics of optical fibers in assemblies of the sort used in analog image communications like CATV (CAble TeleVision), very high speed communications and optical amplifiers, or optical fiber assemblies having isolator functions.
2. Description of the Prior Art
The prior art for connecting two optical fibers with a small connection loss and little light reflected back to the source has been proposed in U.S. Pat. No. 5245684 and Laid-open Japanese Patent Application Nos. 87111/1986 and 121805/1989. The objective is achieved by polishing the ferrule tips of both the fibers to an oblique convex spherical surface and connecting said fibers by bringing these oblique convex spherical surfaces in contact with each other.
For example, referring to FIG. 16, to connect the optical fibers s and s', the end faces of the ferrules f and f' of these optical fibers are polished to form oblique spherical surfaces q and q' in such a way that, the line joining the centers of curvature C and C' of the said oblique spherical surfaces q and q' makes an angle of 8.degree. with respect to the optical axes L and L' of said optical fibers.
The foregoing method improves the coincidence of the optical axes of the fibers s and s' and enables light reflected back to the source to be minimized.
In conventional optical connector end-face polishing methods, the convex spherical surface q is formed according to the procedure mentioned below.
In the beginning, as shown in FIG. 17(a), the optical fiber s and the ferrule f with a cortically tapered tip are bonded by reinforced adhesives.
Next, as shown in FIG. 17(b), the ferrule f is rotated around a vertical axis of rotation after inclining it by an angle of 8.degree. on a polishing disc (not shown in the figure), thereby forming an oblique horizontal surface F at the tip of the ferrule f. Because the ferrule f has a conically tapered tip, the center Ft of the oblique horizontal surface F is offset from the point P where the optical axis of the optical fiber s intersects with the surface F.
Hereafter, as shown in FIG. 17(c), the ferrule f in its inclined position is rotated around a vertical axis of rotation on a polishing disc with an elastic abrasive disc mounted (not shown in the figure) on it, thereby forming an oblique convex spherical surface q at the tip of it.
In the aforementioned conventional method for polishing the end face of the optical connector, the center qt of the oblique convex spherical surface q is offset from the point P, as shown in FIG. 18, because the position of qt, the center of the said surface affects Ft, the center of the horizontal surface F, and because the contact with the polishing disc mounted with an elastic abrasive disc creates an unbalance due to the inclination of the ferrule f (for instance, when the angles at the corners fa and fb are different).